Process and apparatus for producing moulded coke in a vertical furnace which is at least partly electrically heated

ABSTRACT

An apparatus and process for producing coke in a vertical furnace having an upper part for preheating and devolitalizing raw ovoids of coal, an electrically heated median part for carbonizing and coking the ovoids and a lower part for partially cooling the coked ovoids by counter current flow of recycled product gases recovered from the upper part of the furnace. A cooling chamber is connected to the lower part of the furnace for further cooling the coked ovoids by countercurrent flow of a portion of the recycled product gases which are withdrawn after flowing through the partially cooled coked ovoids and introduced into the upper part of the furnace to prevent condensation of condensibles contained in the product gases. The median part of the furnace may be electrically heated by electrodes, induction coils or a combination of electrodes and induction coils.

BACKGROUND OF THE INVENTION

The invention relates to a process for manufacturing moulded coke and avertical furnace for manufacturing said coke in which the heating andcoking heat is provided by an electric supply of energy and transferredby a recycled current of gas. The invention also relates to anelectrical heating process and device untilizing a fluid-conductinggranulated bed.

Processes are known for manufacturing moulded coke in a vertical furnacein which a heap of moulded coal ovoids circulates downwardly in acounter-current manner relative to a recycled current of gas coming froma fraction of the gas produced by the coking and taken from the top ofthe furnace and re-introduced at the base of the latter.

The moulded ovods are coked in a median zone of the furnace by a gaseoussupply from the distillation.

It has been proposed to achieve this supply of heat, initially producedby means of burners, by the dissipation of electrical energy by theJoule effect, which has for result to avoid the dilution of the cokinggases recovered at the top of the furnace by the smoke resulting fromthe combustion, whose volume is large, in particular when the burnersare supplied with air, and thus considerably increase the calorificvalue of the coking gases recovered at the top of the furnace.

In a first manner of tackling the problem, the calorific energy wassupplied by an outer electrical heating, of the electrical resistancefurnace type, however, this technique has a poor yield and efficiency,since the heap of coke is not uniformly heated. Indeed, the cokeundergoes at the walls an excessive overheating which is excessivelyrapid and has an adverse effect on the mechanical behaviour of theovoids (bursting and cracking) and on their metallurgical quality(re-activity).

Various publications, namely the patents FR-A-628,168, US-A-2,127,542,DE-A-409,341 and FR-A-2,529,220, have proposed for solving theseproblems, to supply the calorific coking energy directly in theconcerned zone by supplying electrical energy to the heap of hot ovoidsby generating electrical currents between diametrically opposedelectrodes separated by the heap of ovoids to be coked.

In patent FR-A-2,529,220, the vertical furnace is in the form of acolumn having a cross-sectional shape which is substantially uniformthroughout the inner height of the bed of moulded ovoids in circulation,and comprises, on one hand, electrodes disposed in a median zone of thelateral wall of the furnace, and, on the other hand, movable electrodeswhich are introduced through the upper part of the furnace into the bedof circulating ovoids and disposed in an adjustable manner at a level ofthe furnace higher than that of the fixed electrodes.

One of the major drawbacks of this type of furnace resides in thedifficulty of ensuring an apropriate electrical conductivity of the bedof circulating moulded coal ovoids so as to regulate in a homogeneousand optimum manner the supply of heat required for the coking of theovoids Indeed, the electrical conductivity of the mass of ovoids isrelated, partly, to the quality and the reproducibility of theindividual contacts of the ovoids with one another, and therefore to thedistribution of the internal pressures of this mass obtained bycompacting. Now, an excessive local or general compacting of this bedconstitutes a hindrance to the "fluid" flow of the materials and to acorrect circulation of the bed, which is not acceptable.

Further, the passage of a localized current producing a localizedheating by the Joule effect of the mass of ovoids considerably reducesthe resistivity and results in a concentration of the electricalcurrents in a zone which is already excessively hot.

This difficulty is not suitably mastered by the means describedhereinbefore and the regulation of the thermal equilibrium of thecirculating ovoid bed is not ensured, which is however necessary for thecontrol of the quality of the baking of the ovoids (namely progressive,regular, homogeneous and precise).

SUMMARY OF THE INVENTION

An object of the invention is to overcome these drawbacks by providing aprocess for manufacturing moulded coke in a vertical furnace whosestructure optimizes the distribution of the supply of heating energysuitably distributed throughout the section of the furnace, whileensuring a correct circulation of the mass of coke and achieving optimumconditions of coking of the moulded coal ovoids.

The invention therefore provides a process for manufacturing mouldedcoke in a vertical furnace of the type comprising in its upper partsealed means for introducing a charge of raw moulded ovoids and meansfor recovering the gases produced; and, in its lower part, sealed meansfor discharging the coke and means for introducing a current of gas,which comprises circulating a current of recycled gases in an ascendingflow counter-current to the descending charge of mouledd coal ovoidsconstituting a descending moving bed; subjecting the moulded coal ovoidsto a pre-heating and de-volatilizing step in a first zone correspondingto the upper part of the furnace, then to a carbonizing and coking stepin a second zone corresponding to a median part of the furnace, and to astep for cooling the coked ovoids in a third zone corresponding to thelower part of the furnace; recovering at the top of the furnace the topgases produced by the distillation and the coking of the coal ovoids;and recycling a fraction of said top gases so as to constitute therecycled gas current, characterised in that it comprises introducing afirst part of the fraction of the top gases recycled at the base of thethird zone so as to achieve a primary cooling of the coke and the restof the fraction of the top gases recycled in the form of a secondarycooling current circulating counter-current to the mass of coke issuingfrom the third zone, in a fourth zone connected in a sealed manner tothe outlet of the third zone, thereafter withdrawing the secondarycooling current from the fourth zone and re-introducing said secondarycooling current in the top of the furnace so as to dilute the gasesproduced and maintain the means for recovering said gases at asufficiently high temperature to prevent any condensation; and adischarging the cold coke from the fourth zone through a sealedlock-chamber.

According to other features of the invention:

The terminal coking stage is carried out by dissipation of electricalenergy by the Joule effect in the bed of ovoids which have becomeelectrically conductive, until the desired final temperature is reached.The recycled gases, re-heated by thermal exchange in the final coolingof the ovoids are superheated on the ovoids which are electricallyheated. They convey and transfer this heat in succession in the courseof carbonization, distillation and pre-heating in the upper zones of thefurnace.

The electrical heating is carried out by electrical resistance in themoving bed of coked moulded ovoids of a current generated between atleast two diametrically opposed electrodes placed in the walls of thetank at the level of the second zone.

The electrical heating is achieved by induction of electrical currentsin the moving bed of coked ovoids which fills the lower part of thesecond zone.

The invention also provides a process for manufacturing metallizedmoulded coke, characterized in that it comprises coking, by a processsuch as defined hereinbefore, a charge of moulded ovoids prepared bycompacting a paste constituted by a single or mixed binder of a mixtureof suitable coals, and fine particles of a material based on themetallic element to be incorporated in the coke, in the metallic oroxidized form.

The material based on the metallic element consists of oxides of iron,manganese ore and dust resulting from the production of ferro-manganese,concentrates of chromites for the production of ferro-chromium, quartzfines and silica powders which must be recycled for the production offerro-silicon.

The invention also provides a vertical furnace for manufacturing mouldedcoke which is in the form of a substantially tubular enclosure defininga first pre-heating zone corresponding to the upper part of theenclosure, a second carbonizing and coking zone corresponding to themedian zone of the enclosure, and a third coke cooling zonecorresponding to the lower part of the enclosure, the furnace comprisingat its top sealed means for introducing a charge constituted by rawmoulded ovoids and means for recovering the gases produced, and, at itsbase, sealed means for discharging the coke and means for admitting arecycled gas current, the admission means being connected, outside thefurnace, to means for recovering the gases produced by recycling means,and electrical heating means disposed in the wall of the secondcarbonizing and coking zone, characterised in that the furnace comprisesa fourth sealed secondary cooling zone connected, upstream, to thedischarging means of the third zone and, downstream, to a sealeddischarging lock-chamber, the fourth zone comprising, at its base atleast one conduit for supplyig a cooling secondary gas current connectedto the recycling means, and, at its top, at least one return conduit forthe secondary cooling gases connected to the upper part of the furnacein the vicinity of the means for recovering the gases produced by thedistillation and coking of the coal.

The sealed means for introducing the charge comprise a sealedlock-chamber for supplying the charge and communicating in its lowerpart with the first zone of the furnace through a distribution bell, thesupply lock-chamber being itself supplied by a rotatable hopper.

The means for discharging the coke issuing from the third zone comprisea rotating hearth which is movable in vertical translation andcommunicates, through a sealed lock-chamber, with the fourth secondarycooling zone.

According to a first embodiment of the invention, the electrical heatingmeans are of the electrically resistive type and formed by at least onepair of diametrically opposed electrodes located at the base of the wallof the second zone of the enclosure of the furnace, said wall forming,in this zone, a constriction of the inner section of passage of the bedof moulded ovoids defined by a shoulder against which the fixedelectrodes are mounted.

In a preferred embodiment of the invention, the electrodes comprisesegments whose profile in vertical section is L-shaped extending alongeach side of the shoulder so that one of the branches of the L ishorizontal.

In the case of a vertical furnace having a circular section, theelectrode segments are circular and separated from the others by aninterposed wall of a refractory and insulating material in the shape ofan inclined plane corresponding to the slope of the shoulder defined bythe L-shped profile of the electrodes.

This L-shaped profile is preferably chosen, since it results in anaccumulation in the form of a heap of the coked and highly conductiveovoids on the electrode which they protect. This protective heap isconstantly renewed. It prolongs the electrode while protecting it fromabrasion of the descending moulded coke bed and it isolates the latterfrom the hot baking zone and from the gases of the recycled gas currentwhich are very hot in this region. Consequently, there is a reduction inthermal losses and an improved mechanical resistance of the electrodes,above all when the latter are of cooled copper alloy.

According to a modification of the embodiment of the heating byresistance, the furnace comprises an inner enclosure having an ogivalshape and made from a refractory material provided with a centralelectrode which cooperates with a peripheral electrode which circulatesalong the inner wall of the enclosure. The two electrodes are fed by adirect or a single phase current.

According to a second embodiment of the invention, the electricalheating means are of the induction type and formed by an induction coilcoaxial with the tank and located in the refractory lining of thefurnace.

In a modification, the furnace comprises an inner enclosure having anogival shape and composed of a refractory material, in which is disposeda laminated magnetic core.

The good distribution of the heating energy is still further improved bywinding around this magnetic core an internal induction core which iscoaxial with the external induction coil and fed with current in phasewith the latter by the same source of current at moderate frequency.

According to another modification, the induction heating means areformed by an assembly of pairs of induction coils disposed radially inthe refractory wall of the furnace and defining an external inductorgenerating a rotating field extending horizontally across the tank.

According to a modification of this last-mentioned embodiment, adated tofurnaces of large diameter, the furnace comprises an inner ogival-shapedenclosure made from a refractory material in which is disposed aninternal inductor constituted by an assembly of radial coils disposed infacing relation to the coils of the external inductor and determining anassembly of pairs of coupled coils which cooperate for the generation ofa rotating field between the external inductor and the internalinductor.

According to a further mixed embodiment, the electrical heating meansare formed by the combination of at least one pair of electrodes such asdescribed before, generating heat by electrical resistance and at leastone coil gnerating heat by induction.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described hereinafter in detail with reference tothe accompanying drawings which show several embodiments of theinvention. In these drawings:

FIG. 1 is a diagrammatic axial sectional view of a vertical cokingfurnace according to the invention;

FIG. 2A is a horizontal sectional view taken on plane 2--2 of FIG. 1 ofa first modification having two pairs of electrodes fed by a two phasecurrent source (Scott transformer);

FIG. 2B is a diagram of the principle of operation of the feed of theelectrodes of FIG. 2A;

FIG. 3A is a horizontal sectional view taken on plane 2--2 of FIG. 1 ofa second modification having three pairs of electrodes fed by a triphasecurrent source;

FIG. 3B is a diagram of the principle of operation of the feed of theelectrodes of FIG. 3A;

FIG. 4 is a vertical radial sectional view taken on line 4--4 of FIG. 3Aof the wall of the furnace in the zone of an electrode;

FIG. 5 is a radial and vertical sectional view taken on line 5--5 ofFIG. 3A of the wall of the furnace;

FIG. 6 is a perspective view of a battery of three coke furnace unitsaccording to the invention in a modification having a rectangularcross-sectional shape with three pairs of opposed electrodes fed withthree phase current;

FIG. 7 is a partial axial sectional view of the lower part of amodification of the furnace of FIG. 1 with a single phase current supplyor a dc supply;

FIG. 8 is a horizontal sectional view taken on plane 8--8 of the furnaceof FIG. 7;

FIG. 9 is a diagrammatic partial vertical axisl sectional view of asecond embodiment of the furnace according to the invention which isheated by simple induction;

FIG. 10 is a diagrammatic partial vertical axial view of a secondembodiment of the furnace of FIG. 9 with heating by exterior and axialinduction;

FIG. 11 is a diagrammatic pertial vertical axial sectional view of athird modification of the furnace of FIG. 9 with heating by exteriorinduction with rotating fields;

FIG. 12 is a diagrammatic partial vertical axial sectional view of afourth modification of the furnace of FIG. 9 with heating by exteriorand interior induction with rotating fields

FIG. 13 is a diagrammatic horizontal sectional view taken on plane13--13 of the furnace of FIG. 12 illustrating the principle of theconnection of the inductors;

FIG. 14 is a diagrammatic partial view of a mixed embodiment of theinvention with heating by single phase electrical resistance heating andexterior electromagnetic induction.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The process of the invention comprises coking in a continuous manner ina vertical furnace heated electrically by resistance and/or inductionovoidsor balls of dried coal agglomerated by binders and press-moulded.

The pyrolysis of the ovoids in the furnace results in the emanation ofgases of distillation of the coals and the binders, a large part ofwhich is recycled to the base of the furnace after a rough purification.These recycled gases form an ascending gas current which cools theovoids in thelower part of the furnace and progressively heats, in acounter-current manner, the ovoids which descend the upper part of thefurnace.

The ovoids are successively pre-heated and dried and then the fumes areremoved therefrom. The carbonization then ensures the mechanicalconsolidation of the ovoids

The progressive heating of the ovoids completely eliminates the volatilesubstances at around 850° C. and the ovoids then become sufficientlyconductive of electricity to function as electrical resistance heaters,when an electrical current is supplied to them. This resistivity is usedfor passing through the bed of ovoids electrical currents which heat theovoids by the Joule effect within their mass and at the points ofcontact therebetween.

This electrical heating completes the baking and coking of the ovoids atthe desired temperature.

The bed of ovoids then behaves in the manner of a heating grate whichsuperheats in a counter-current manner the ascending gas current issuingfrom the lower part of the furnace in which the coked ovoids are cooled.

This superheating of the gas also has for effect to crack the heavyhydrocarbons still contained in the gas. The ascending gas current isthusmainly constituted of hydrogen (and methane). Owing to itsparticular thermal and electrical properties, it constitutes anexcellent vehicle forexchange of heat between the gases and the ovoids,

which avoids the formation of arcs and sparking between the ovoids.

The raw moulded ovoids or balls are prepared by first of all making up apaste of a mixed binder (resin, tar, asphalt ...) and the previouslymixed, dried, crushed and pre-heated coals. The pre-heated paste is thencompacted in the form of ovoids or balls in a press having tangentialcylindrical hoops.

The vertical furnace shown in FIG. 1 comprises a metal shell or casing1' provided on its inner surface with a refractory lining 2' defining asubstantially tubular enclosure 3, which is slightly frustoconical inits upper part, in which there is charged a mass of moulded ovoidsconstituting the moving bed. In the embodiment shown in FIG. 1, theenclosure 3 has a circular section, but it may also have a rectangularsection, as illustrated in FIG. 6.

The vertical furnace is charged at its upper end by sealed means forintroducing the raw moulded ovoids which comprise a rotating hopper 5fed with ovoids by a belt conveyor 6 controlled by a detector 7 of thelevel of the charge placed in the hopper. The hopper 5 includes in itslower part a rotating bell 8 the opening of which, under the control ofa jack 9, causes the introduction of the ovoids into a sealedlock-chamber 10 comprising conduits 11a, 11b for purging by means ofneutral gas. The sealed lock-chamber 10 is closed in its lower partopening into the furnace by a distribution bell 12 the opening of whichis controlled by a jack 13 as a function of indications from a detector14 of the level of the charge placed at the top of the vertical furnace.

The opening of the bells 12 and 8 is effected in sequence as a functionof the indications of the detector 14.

The furnace is also provided at its upper end with means for recoveringthegases produced which are constituted by two ducts 15a, 15b of largediameter opening into the enclosure of the furnace on each side of therotating distributing bell 12.

The coking gas recovered by the ducts 15a, 15b is sent to a primarypurifying installation diagrammatically represented at 16 so as to besubjected to a treatment including cooling, washing, removal of tar anda summary condensation of water and naphthalene. The gas treated in thiswayis recycled in respect of a fraction of 60 to 80% thereof to thefurnace through recycling conduit 17 and sent in respect of theremaining fractionthrough the conduit 18 to a storage gasometer (notshown) through a conventional secondary purifying installationdiagrammatically shown at 19.

The enclosure 3 of the furnace comprises three distinct operating zones.The upper part of the enclosure corresponds to a first baking zone 20where the ovoids are gradually pre-heated and rendered smokeless bydistillation of the coals and binders and undergo a first carbonizationstep by the ascending hot gas current flowing in a counter-currentmanner.

The median part corresponds to a second zone 21 of the end of thecarbonization and coking at the base of which are installed theelectricalheating means 22 disposed in the inner wall of the refractorylining 2'.

A third zone 23 for effecting a primary cooling of the coke formedoccupiesthe lower part of the enclosure and includes at its base inletmeans for a gas current recycled from the primary purifying installation16. These means comprise a group of inlet conduits 24 for the primaryrecycled current issuing from a circular supply ring 25 connected to therecycling conduit 17 through a conduit 26 in which is mounted a valve 27for regulating the flow and controlled as a function of the indicationsdelivered by temperature detectors 28 located at the top of the furnace.The circulation of the recycled gas in the conduit 17 is ensured by ablower 29 and the inlet flow of a first part of the recycled gas,corresponding to a primary current, sent into the conduit 26, isregulatedin such manner as to maintain the temperature detected by thedetectors 28 at a predetermined set value, so as to avoid condensationof tars on the charged ovoids and on the inner walls of the furnace.

The furnace has at its base means for discharging the coke coming fromthe third zone 23, which comprise a rotating hearth 30 driven inrotation by amotor speed-reducer unit 31 and movable in verticaltranslation by means ofa jack 32 for adjusting the height thereof.

The rotating hearth 30 puts the third zone 23 of the furnace incommunication with a lock-chamber 33 which opens into a fourth zone 34foreffecting a secondary cooling of the coke.

The secondary cooling fourth zone 34 comprises at its base inletconduits 35 for a secondary current for cooling corresponding to theremaining partof the recycled gas current. These conduits 35 extend froma circular ring 36 connected through a conduit 37 and a flow regulatingvalve 38 to the recycling conduit 17. The valve 38 is controlled inaccordance with the indications delivered by a temperature detector 39which measures the meantemperaure of the coke of the fourth zone 34effecting the secondary cooling of the coke. The flow of the remainingpart of the recycled gases introduced in the form of a secondary coolingcurrent is regulated in suchmanner as to maintain the temperature of thecoke detected by the detector 39 at a predetermined set value lower thanthe maximum temperature of the normal handling of the coke.

This secondary cooling fourth zone 34 comprises in its upper partconduits 40 opening into a circular manifold 41 of the secondary coolingcurrent which is connected through a pipe 42, in which is mounted ablower 43, to a circular ring 44 for the return of the secondary coolingcurrent surrounding the upper part of the furnace where there arerecovered the gases produced which enter this circular ring 44 throughreturn conduits 45.

The cooling fourth zone 34 is connected, on the downstream side, tosealed lock-chamber 46 provided with purging conduits 47, 48 andconnected to a discharge hopper 49 which releases the cold coke onto anextracting and metering belt device 50.

The sequential and automatic opening of the valves 51, 52 and 53ensuring the communication between the lock-chamber 33, the fourth zone34 and the sealed lock-chamber 46, is controlled respectively by jacks54, 55 ad 56 in accordance with the indications delivered by a detector57 of the charge level located at the top of the fourth zone.

The structure of the furnace just described permits, by means of itsdevicefor recycling the gases divided into a primary current and asecondary current, on one hand, the optimization of the thermal profileof the furance in the carbonization zone by the regulation of theprimary current, and, on the other hand, the avoidance of anaccumulation of condensable tars in the upper part of the verticalfurnace owing to the face that the temperature at the top of the furnaceis maintained at at least 150° C. and to the entrainment of these tarsby dilution in the secondary current extracted from the cooling fourthzone.

The ovoids or balls leaving the first zone reach a temperature of about850° C., beyond which the electrical conductivity becomes appreciableand considerably increases to a limit value at about 1,100° C.

It is in the lower part of the secondary zone, where temperatures higherthan 900° C. prevail, that the electrical currents are applied ofinduced which superheat the ovoids up to the final coking temperature,setat 950° to 1,250° C., depending on the reactivity of the cokethat itis desired to produce (1,100° C. in respect of a metallurgical coke).

The coked ovoids descend in the lower part of the furnace correspondingto the third primary cooling zone 23, at the base of which is injectedthe recycled cold gas current which is used as a thermal transferringmeans inthe various zones of the furnace.

After cooling, the coked ovoids extracted continuously from the thirdzone by means of a rotating hearth are discharged in two stages. In afourth zone for effecting the secondary cooling of the coke, the ovoidsare completely cooled by a recycled gas secondary current which isthereafter sent back to the top of the furnace; then they are removedfrom the furnace through the final lock-chamber purged with neutral gas,which eliminates any risk of explosion. The moulded coke is extracted inthe cold state and then screened before expedition.

As compared with the coke produced in a battery of conventionalfurnaces, the manufacture of moulded electrical coke combines theadvantages of cokebaked by means of gas with those of the electricalprocess.

First of all, as compared with the conventional coke, the manufacture ofthe moulded coke has the following advantages:

Diversification of the supplies of coals and reduction in the cost priceofthe coke paste.

The process permits the massive use of anthracite, lean coals, inerts,cokedust, petroleum coke and the substitution of fusible melting coalsby binders, such as resins, tars and asphaltic residues.

The decentralization of the production of the coke.

The process permits the production of moulded coke with smaller unitsadapted to the needs of quantity and quality (shapes, dimensions, bakingtemperature and reactivity of the coke).

The reduction in the investment costs of more than 20% for a givenproduction.

A much higher thermal efficiency, since the top gases issue at about150° C. and the ovoids are extracted in the cold state from the tankfurnace while, in a conventional battery, the gases issue at 500° C.,the coke is discharged from the furance at more than 1,000° C. and thesmoke is at a temperature of more than 400° C. at the chimney.

An improved yield of the coke, since the dry cooling of the ovoids inthe neutral gas does not oxidize the carbon of the coke as does thesteam of the conventional wet extinction.

Further, as compared with moulded coke baked in a gas flame, theelectric moulded coke has the following advantages:

The production of a rich distillation gas without heavy hydrocarbons,sincethe gas is not diluted in the combustion smoke and the recyclingcauses thecracking of the hydrocarbons. This gas can be valorized asfurnace fuel or for extracting the hydrogen it contains.

An excellent yield of coke due to the absence of any combustion and/orsurface oxidation of the ovoids in the furnace.

The control of the physical and chemical quality of the coke.

The combination of the electrical heating and the reycled gascounter-current results in a progressive coking with a precise controlof the temperature of the various zones:smoke removal and pre-baking,carbonization and electric coking, cooling of the ovoids.

The homogeneity of the baking temperature ensures the regularity of thequality of the coke.

The control of the baking temperature permits the mastering of thereactivity of the coke produced:reactive coke for electrometallurgy(bakedat low temperature), foundry coke with a very low reactivity(baked at hightemperature: 1,300° C.), blast-furnace coke having anadjusted reactivity.

The choice of the size of the coke.

The supply of electrical energy to the coking front in each ovoidpermits aprogressive internal baking in the high temperature zone. It ispossible toproduce cokes having a larger size which are homogeneous andare more suitable for the blast-furnace or the cupola, since theirstrength is distinctly better than that of ovoids baked with gas.

The low inertia of the furnace.

The rapid electrical control of the heating permits adaptation tochanges in the coking rate, the corrections the malfunctions (baking)and facilitates starting up and stopping.

The absence of pollution and improved working conditions.

The extraction of the ovoids is effected in the dry state. The furanceis sealed when charging and discharging the furance. The pollution ofthe atmosphere is therefore limited and the working conditions areconsequently considerably improved.

The possibility of employing small and medium size units.

The small units produce on the site the desired quantity and quality ofthecoke and may be economic since they may be automated and are notheavily penalized by a higher investment.

The heating means 22 disposed in the lower part of the second zone 21correspond to two embodiments which will now be described.

According to a first embodiment corrsponding to an electrical heating ofthe resistance type, the inner wall of the refractory lining 2' definingthe enclosure 3 forms a narrowing of the internal section of the passageof the bed of moulded ovoids to the lower part of the second zone 21.Thisnarrowing is defined by a shoulder 58 formed along the wall of theenclosure 3.

As is in particular shown in FIG. 4, electrodes 59 having a profile invertical section in the shape of an L extend along each side of theshoulder 58 so that one of the branches of the L is horizontal. Theelectrode 59 is of an electrically conductive material, for examplecopper, and fixed by a rod 60 extending therethrough and the refractorylining 2', to the exterior of the half-shell 1' by conventional meanssuchas a nut and a lock-nut. The rod 60 is electrically insulated fromthe shell 1' by interposition of an electrically insulating material inthe form of discs 61. The end of the rod 60 outside the shell forms aterminal62 to which is fixed an electrical supply 63 for the electrodeconnected tothe source of current 64 shown in FIG. 1.

The refractory lining zone 2' immediately adjacent to the electrode 59is cooled by a tube 65 having an internal circulation of cooling fluiddisposed as a coil along the two sides of the electrode 59 in front oftherefractory lining. The electrode may also be cooled directly by theinternal circulation of the cooling fluid. In the case of a verticalfurnace having a circular transverse cross-sectional shape shown inFIGS. 2A and 3A, the electrodes 59 are in the form of diametricallyopposed circular segments separated from each other by an interposedseparating wall 66 which can be more clearly seen in FIG. 5. This wall66 is in the shape of an inclined plane having an inclinationcorresponding to the slope of the shoulder 58 against which theelectrodes 59 are mounted.

According to a first modification of the first embodiment using a supplyatthe frequency of the mains, there is disposed around the tank a pairof elecrodes 59 per phase. The electrodes of a given phase arediametrically opposed in the tank, as shown in FIGS. 2A and 3A, so as toensure the passage of the current to the centre of the furnace. Theirsupply voltage is adjustable (phase by phase) by acting on the secondarywinding of the supply transformer.

According to the dimension of the furnace, there is place for disposingthenecessary two or three pairs of electrodes on the periphery of thefurnace.

For furances of small diameter, for example less than or equal to 2 m, atwo phase supply is provided such as that illustrated in FIGS. 2A and 2Bby means of a Scott transformer in accordance with the connectiondiagram of FIG. 2A, which transforms a three phase primary supply into atwo phasesecondary supply (phases carrying the references 1 and 1b, onone hand, and2 and 2b, on the other) of adjustable voltage.

In the case of furnaces of larger diameter, for example 3 to 4 m,illustrated in FIGS. 3A and 3B, the three pairs of electrodes carryingthereferences 1, 1b; 2, 2b; 3, 3b are supplied with power in accordancewith the three phase diagram of FIG. 3B.

The electrodes 59 constituted by circular segments the section of whichis in the shape of an L, bear inside the furnace on a cooled refractoryledge67 (FIG. 4). There forms on each of these electrodes a natural heapof highly graphitized ovoids (by localized supercoking brought about bythe prolonged stay of the ovoids at high temperature) which are veryconductive and protect the electrodes 59 and distribute the currentdensities in the ascending charge.

Each electrode is separated from the neighbouring electrode by aninsulating refractory interposed wall 66 which resists abrasion (forexample silicon carbide bricks with a silicon nitride binder) the taperofwhich results in a slight progressive compression of the charge in theregion of the copper electrodes so as to improve the homogenize theelectrical conductivity of the bed of ovoids in the course of coking.

On the other hand, under the compressed coking zone, at the entrance oftheprimary cooling zone 23, the diameter of the furnace rapidlyincreases so as to reduce the compression of the bed of ovoids, increasethe electricalcontact resistances between the ovoids and avoid parasiticcurrents in the cooling zone where they would heat the already-cokedovoids at a shear lost. The developed width of the circular segments ofthe electrodes 59 ischosen to be approximately equal to the width of theinterposed refractory walls 66 so as to avoid preferential passagesbetween phases or even shorting from one phase to the other on theperiphery of the furance.

The present invention has been described hereinbefore with reference toa furnace whose vertical chamber has a circular transversecross-sectional shape. FIG. 6 shows a modification in which thecross-sectional shape of the tank is rectangular.

The structure of this furance is substantially similar to that describedwith referece to FIG. 1 as concerns the means for introducing the chargeof raw moulded ovoids or balls and the recovery of the coke, and asconcerns the recycling of the coking gas recovered through twocollecting ducts 70 and 72 located at the top of the furnace andreturned to the baseof the primary cooling zone through two conduits 72and 73. In this case also, the cooling of the coke occurs in two stagesbetween which the fractions of the recycled gases are divided aspreviously explained.

As essential difference resides in the linear shape of the electrodes 74for conducting electric current which are disposed on two opposed sidesofthe rectangular section and rest on ledges 75. These electrodes alsohave and L-shaped profile on which accumulates a heap of highlygraphitized ovoids.

For an application of indusrial interest with a triphase supply, thefurnaces are grouped in three units as shown in FIG. 6. Each currentphasesupplies power from a transformer 76 to a pair of copperelectrodes. The electrodes of a given phase are disposed in facingrelation to each other along each of the large sides of the furnace andare separated from the adjacent pair of electrodes by an insulatingrefractory wall 77.

In a modification of the first embodiment of the invention illustratedin FIGS. 7 and 8, the circular furnace comprises an inner enclosure 80of ogival shape and made from are fractory material, whereas thestructure ofthe enclosure 3 of the furance remains identical in all itsperipheral parts. This enclosure 80 carries a central frustoconicalelectrode 81 which ensures the return of the currents passing throughthe mass of hot ovoids in process of coking and coming from a circularperipheral electrode 82 having an L-shaped section extending along theinner periphery of the tank above the ledge 67.

This arrangement is intended to avoid parasitic currents between theelectrodes supplied by different phases and to ensure the passage of thecurrent to the centre of the furnace. The supply is ensured, between theperipheral electrode 82 connected as an anode and the central electrode81forming a cathode, by a direct current source, for example a rectifier83, or a single phase current source for a furnace of small capacity.

The ogival enclosure 80 is mounted on a rod 84 extending through thecentreof a column 85 ensuring the support and the mobility of theannular rotating hearth 86.

In order to adjust the height of the electrical coking zone, the ogivalenclosure 80 is vertically movable under the action of a jack 87 placedunder the rod 84. In its upper part, the rod 84 is surmounted by aninsulator 88 which prevents the passage of parasitic return currentsalongthe rod 84.

The central electrode 81 in the shape of a truncated cone is made from amaterial which resists abrasion, such as densified silicon carbide whichis sufficiently conductive of electricity to limit the localized heatingof the walls of the cathode 81. The cathode 81 bears on a sleeve 89 of arefractory insulating material. The currents returning through thecathode81 travel down to the base of the furnace through an insulatedcooled conductor 90 disposed in an axial bore of the rod 84.

The column 85 is slidably mounted, for example by a system of splines(not shown), in a bevel gear wheel 91 for driving the column in rotationby means of a bevel gear pinion 92 engaged therewith, the pinion 92being mounted on the end of an output shaft of a motor-speed reducerunit 93. The vertical sliding of the column is ensured by a jack 94. Therate of extraction of the coke, which is homogeneous throughout theperiphery, is regulated by adjusting the speed of rotation of themetering hearth and the height of the latter.

The cathode 91 is cooled by a circulation of a cooled gas current from aconduit 95, this gas excaping through the annular gap provided betweentheogival enclosure and the column 85 in the region where the enclosure80 is placed over this column.

According to a second embodiment, illustrated in detail in FIGS. 9 to13, the electrical heating is ensured by induction.

As shown in FIG. 9, the heating means disposed at the base of the cokingzone 21 comprise an induction coil 100 coaxial with the enclosure 3 anddisposed in the refractory wall 2' of the furance. Mild steel cores 101,verticaly laminated, are disposed radially around the coil 100 andcanalize the return lines of the field. The coil 100 is supplied withcurrent by a generator 102 supplying a moderate frequency between about50and 1,000 Hertz.

The electric conductor which constitutes the coil 100 is a hollow tubein which circulates a cooling fluid introduced at 103 and drawn off at104, which is itself connected by conductors 105 and 106 to thegenerator 102.

The laminated cores 101 constitute a magnetic yoke cooled by circulationofa cooling fluid introduced through the conduit 107 and drawn offthrough the conduit 108.

The expression of the voluminal power (dissipated electrical powermultiplied by the unit volume of coke) established for the embodiment ofFIG. 9, shows that the radius of the vertical chamber and theconductivityof the ovoids or balls have a determinant influence on thepowers developedlocally in the bed.

In particular, as the induction fields are weak at the centre of thefurnace, this first embodiment has the drawback of unequally heating theballs which pass alongside the wall and those which pass alongside thecentre of the furance which are liable to be insufficiently heated.

In the case of large-capacity furnaces (diameter of 3 m and more) inrespect of which the ascending gas current would have a limitedeffectiveness in the reduction of the transverse heterogeneities in theheating, the beds of ovoids disposed adjacent the exterior would have atemperature and an electric conductivity substantially higher than theovoids at the centre, which would result in different temperatures atthe end of the coking, and an unequal quality of the coked ovoids at thecentre and at the wall.

This simple solution shown in FIG. 9 is therefore limited to smallcoking units whose extracting device will favour a peripheral flow ofthe ovoids (for example, rotating hearth).

According to a modification of the second embodiment illustrated in FIG.10, the furnace comprises electrical induction heating means whichfurthercomprise an induction coil 110 coaxial with the enclosure 3 anddisposed inthe refractory wall 2' of the furnace, an inner enclosure 111having an ogival shape and made from a refractory material whichincludes means for reinforcing the magnetic field in the vicinity of theaxis of the furnace.The refractory material constituting the enclosure111 may be, for example,silicon carbide with a binder of siliconnitride, whose properties of electrical insulation are sufficient forthe envisaged application and whose resistance to abrasion and tothermal shocks is excellent.

These means may be formed by an assembly of vertically laminated mildsteelcores 112 disposed radially and mounted in the ogival-shapedenclosure 111.

These means may be completed, as illustrated in FIG. 10, by an internalinduction coil 113 coaxial with the coil 110, supplied in phase with thelatter and located in the ogival-shaped enclosure 111. The verticallylaminated mild steel cores 112 disposed radially are inserted in thecoil 113 coaxially with the latter.

As in the case shown in FIG. 10, the induction coil 110 is formed by ahollow electric conductor wound helically and in which circulates acooling fluid introduced at 114 and drawn off at 115. The internalinduction coil 113 is made in the same way and cooled by the circulationof a cooling fluid between the inlet 116 and the outlet 117. Thiscooling circuit leads to the exterior of the furnace by circulation in acolumn 118 of a diameter smaller than the diameter of the ogival-shapedenclosure111 and supporting the latter. The column 118 extends throughthe rotating hearth of the furance as illustrated in more detail inrespect of the first embodiment of the induction heating represented inFIG. 7.

The assembly of laminated cores 113 constitutes an internal inductionyoke also cooled by the circulation of a cooling fluid supplied by acentral conduit 119 disposed along the axis of the column and leading tothe top of the cores, the fluid being returned through a conduit whichis coaxial with and outside and conduit 119.

Vertically laminated cores 120 are disposed radially outside the coil110 and form an exterior induction yoke cooled by a circulation of acooling fluid supplied through a conduit 121 and drawn off through aconduit 122.

A moderate frequency generator 123 supplies in series the coils 110 and113through a conductor 124 connected to the input of the coil 110, thena conductor 125 connecting the output of the coil 110 to the input ofthe coil 113 and a conductor 126 connecting the output of the coil 113to the generator 123.

The coils 110 and 113 disposed in the furnace in facing relation to eachother permit the association of their respective induction fields forsimultaneously heating in a homogeneous manner the ovoids or ballspassingalong the peripheral walls of the enclosure 3 and the walls ofthe interiorenclosure 111.

In yet another modification of the second embodiment, the inductionheatingmeans are constituted by a group of pairs of induction coilsdisposed radially in the refractory wall of the furnace and thusdefining an external inductor generating a rotating field horizontallyacross the tank.

In FIG. 11, two coils 130, 131 having their axes co-incident anddisposed radially and diametrically opposed, are wound on horizontallylaminated magnetic steel cores forming inductors 132,133. The coils 130and 131 are supplied by the same phase of a polyphase current having thereference numeral 1 so that the magnetic field radially crosses thetank, i.e. the confronting end faces of the coils 130, 131 are ofopposite polarities.

In the normal case of a triphase current, three pairs of diametricallyopposed coils are employed.

Each pair of coils 130, 131 which represents one phase is evenly offsetin the inductor so that the resulting field rotates at the frequency ofthe supply currents and generates Foucault currents in the mass of cokedovoids or balls.

The inductors 132, 133 are cooled by the circulation of a cooling fluidsupplied by a circuit entering through the conduit 135 and issuingthroughthe conduit 136.

A medium frequency triphase generator 137 supplies the coils as shown inFIG. 11 in respect of two coils in an axial sectional plane.

The horizontal section shows the supply which is arranged as indicatedin FIG. 13 with reference to only the inductors outside the enclosure ofthe furnace.

According to yet another modification derived from that illustratedpreviously and shown in FIGS. 12 and 13, the furnace further comprisesan interior enclosure 140 having an ogival shape and made from arefractory material in which is disposed an internal inductorconstituted by a group of radial coils disposed in facing relation tothe coils of the external inductor and determining a group of coupledpairs of coils which cooperateso as to generate a rotating fieldradially between the external inductor and the internal inductor.

Associated with a coil 130 of the external inductor is a coil 130a whichissupplied in such manner that the confronting end faces of the coilshave opposite polarities. Likewise, a coil 131a is associated with thecoil 131.

The coils 130a and 131a are wound on a horizontally laminated magneticsteel inductor through which passes a cooling circuit constituted bycentral supply tube 141 and peripheral return tubes 142 (FIG. 13).

In a mixed modification shown in FIG. 14, the electrical heating meansof the furnace comprise, in the coking zone, electrical resistanceheating means with an L-shaped peripheral electrode 150 and a centralelectrode 151 such as those described with reference to FIG. 7 andsupplied by a rectifier 152, and induction heating means comprising anaxial coil 153, such as those described with reference to FIG. 9 andsupplied by a medium frequency current source 154 and optionally a groupof vertically laminated mild steel cores 156 disposed radially andlocated in the support column 157 of the electrode 151, such as thosedescribed with reference to FIG. 10.

The axial coil 153 is then disposed in the projecting ledge 155, onwhich bears the electrode 150, and below the latter.

This mixed arrangement combining an induction heating on the peripheryof the tank combined with a resistance heating at the centre is intendedfor medium and large capacity furnaces. It associates:

an induction heating by a simple coil coaxial with the tank disposed intherefractory lining of the furnace; this coil, which is identical tothe basic arrangement proposed for the induction heating of FIG. 9,ensures the heating of the external layers;

a resistance heating (by a single phase source or a direct currentsource) of the bed of ovoids between a central electrode and a circularelectrode,such as described with reference to FIG. 7; this arrangementconcerns the fluxes of current toward the electrode around which theovoids are heated,since there is developed, in this region, by adecrease in the section, a greater current density and a greatervoluminal power.

This associated of an induction coil with an electrical resistanceheating between a central electrode and a peripheral electrode alsopermits a rapid rotation of the currents by action on these currents ofthe field lines created by the exterior coil.

In this way, the lines of current between the two electrodes areconstantlyrenewed and the preferential passages of the current along thelines of ovoids which are the most conductive which result in localizedoverheating, are avoided.

The induction heating employs variable fluxes generated by inductioncoils completely outside the mass of ovoids being coked and avoids inlarge partthe problems of variation in the resistance of contact betweenthe ovoids and contact of the ovoids with the electrodes.

The effects of a plurality of coils may be associated in such manner asto control the induction flux lines in the electrical coking zone. Thesepossibilities enable the heating currents to be uniformly distributed inthe transverse section and to avoid the localized overheating of theovoids close to the coils and the parasitic heating currents outside thebaking zone.

Owing to these specific advantages, the electromagnetic inductiondevelopedin a bed of ovoids allows voluminal power levels which varywithin wide limits. For an electrical gradient of 75 to 100 volts permeter, the developed power may reach 5 to 10 megawatts per cubic meterof hot and coked ovoids, whereas it is considerably lower by electricalresistance.

This electric power, higher than the sole thermal requirement ofelectricalcoking, developed in the mass of ovoids, may be used forreducing, by the carbon of the coke and by the volatile substances ofthe binders, fines ofores or oxidized dusts which may be incorporatedwithin composite ovoids orballs.

These reducing reactions, which are developed simultaneously with theelectrical coking, regulate the electrical coking temperature of theovoids and produce a very strong metallized coke.

The present invention encompasses a process for manuturing moulded cokewhereby it is possible to add to the mixture of coals to be compactedintoovoids or balls:

Fines and dust of iron oxides (concentrated, steel work dust andblast-furnace gas, dust from installations for removing dust fromagglomerations of ores, etc . . .).

Fines of manganese ores and dust of ferromanganese production.

Chromite concentrations for the production of ferro-chromium.

Silica and quartz fines recycled in the production of ferro-silicon.

For these various applications, the amount of mineral fines incorporatedinthe coke paste is limited by the electrical conductivity of the bed ofovoids or balls which may not be lower than 100 mhos (electricalconductivity of the homogeneous medium equivalent to the bed of ovoidsat the starting temperature of electrical coking, namely 850° C. to 900°C.).

The invention, as described hereinbefore, also relates to a process anddevice for dissipating in a uniform and homogegeneous manner largevoluminal electric powers developped by the Joule effect of the inducedelectrical currents in a conductive granulated medium which may thus bebrought to a high temperature.

This granulated bed has a large specific surface area and may be usedfor heating or superheating gases, liquids, or melting solids andvaporizing liquids by superheating the vapours thus produced.

The conductive granulated bed is constituted by sufficiently conductiverefractory materials which are in calibrated pieces, particles, or solidor hollow and tubular cylindrical elements, rings, balls or pellets, orsmall bricks.

By way of examples, the refractory materials making up the conductivegranulated bed may be constituted by calibrated pieces and particles ofcarbon, graphite, cokes, or by rings, pellets and cylinders of siliconcarbide, molybdenium silicide, zirconium diboride, or by balls, pellets,small bricks of pastes of coal and cokable mixtures.

For the purpose of its utilization, the granulated bed is chosen as afunction of its electric resistivity, its refractory quality, itsspecificsurface area and its permeability, and lastly its resistance tooxidation and corrosion for the use to which it is put.

As examples of utilization there may be mentioned:

(a) heating of gases

heating and superheating of reducing gases on a bed of calibrated cokepieces;

regeneration and generation of reducing gases by conversion into H₂ andCO of the H₂ O and CO₂ contained in the gas on a coke bed at800° to1000° C.;

cracking and oxidation of the heavy hydrocarbons contained in the rawand damp cokery gas on a coke bed at 900° to 1000° C. for producing in asingle step the thermal "purification" of the raw and hot cokery gas byeliminating all the condensable products;

superheating to 1200° C. reducing gases intended for the "direct"reduction of iron oxides on a coke bed;

superheating to a high temperature of 1200° to 1350° C. of preheatedair, optionally under pressure and superoxygenated as the wind of ablast-furnace on a bed of conductive tubular elements of silicon carbideor molybdenum silicide in the the form of rings.

(b) heating of conductive or insulating liquids, running over conductivegranulated beds which are inert with respect to the liquid such as:

manufacture of dry superheated steam on a bed of cuttings or swarf ofstainless and refractory steel;

superheating of liquid metal running over a bed of coke;

pasteurization of milk.

(c) Fusion of non-conductive solids, for example slags or glass-making"composition" on a "grill" of red coke. The viscous liquid running overthe coke is heated and fluidized.

To carry out the process of preheating gas a furnace is used whichcomprises heating means such as those shown in FIG. 7 to 14.

The conductive granulated bed is compacted in a tubular enclosure of thefurnace whose walls are lined with insulating refractory elements. Thisgranulated bed rests on a refractory grill through which the gas to besuperheated is blown. It may also be placed between two layers ofnonconductive materials such as sand so as to center the escape lines.

We claim:
 1. A process for manufacturing coke, comprising:providing avertical furnace having a tubular enclosure with an upper part, a medianpart and a lower part; the upper part including at an upper end alock-type sealed charging inlet for raw ovoids of coal, an outlet forrecovery of product gases, and an inlet for secondary recycled gas; themedian part including a heater; and the lower part including at a lowerend a lock-type sealed discharging outlet for coke, and an inlet for afirst stream of primary recycled gas; a cooling chamber having an inletat one end connected to said discharging outlet of said lower part ofsaid vertical furnace, a lock-type sealed discharging outlet at an endopposite said one end for cold coke, an inlet at said opposite end for asecond stream of primary recycled gas, and an outlet at said one end forsecondary recycled gas; a first conduit connected to said outlet forrecovery of product gases ad conducting off a portion thereof as aproduct; a second conduit by which said outlet for recovery of productgases is connected to said inlet for said first stream of primaryrecycled gas; a third conduit by which said outlet for recovery ofproduct gases is connected to said inlet for said second stream ofprimary recycled gas; and a fourth conduit by which said outlet forsecondary recycled gas is connected to said inlet for secondary recycledgas; providing a supply of raw moulded ovoids of compacted coal andcharging the ovoids into said upper part of said vertical furnacethrough said sealed charging inlet to provide a bed which descendsthrough said furnace while operating said heater and circulating thefirst stream of primary recycled gas through said furnace countercurrentto said bed descending in said vertical furnace and preheating anddevolatilizing the descending bed in a first zone corresponding to saidupper part of said furnace, carbonizing and coking the descending bed ina second zone corresponding to said median part of said furnace, andcooling the descending bed in a third zone corresponding to said lowerpart of said furnace; passing the descending bed out of said furnaceinto said cooling chamber as partially-cooled coked ovoids to provide adescending bed of partially-cooled coked ovoids therein whilecirculating the second stream of primary recycled gas through saidcooling chamber countercurrent to said descending bed and furthercooling the bed of partially-cooled coked ovoids in a fourth zonecorresponding to said cooling chamber, and passing the coked ovoids outof said cooling chamber as cold coke, and withdrawing secondary recycledgas from the cooling chamber and introducing the withdrawn secondaryrecycled gas into the upper part of the furnace; and recovering productgases produced during devolatilization, carbonizing and coking of thebed of ovoids from the upper end of said upper part of said furnacewhile maintaining the product gases at a temperature which issufficiently high to prevent condensation of tar, water and naphthalenecontained therein by admixture with the secondary recycled gas.
 2. Theprocess of claim 1, including:carbonizing and coking said bed in saidsecond zone by applying electrical energy to said bed using said heater,thereby heating said bed and said gases flowing countercurrent to saidbed in said second zone.
 3. The process of claim 2, wherein:said heaterincludes at least two separated electrodes, and electrical energy isapplied to said bed by passing an electrical current between saidelectrodes via said bed and thereby resistively heating said bed.
 4. Theprocess of claim 1, wherein:said heater induces an electric current insaid bed and thereby inductively heats said bed.
 5. The process of claim2, wherein:the step of providing a supply of raw, moulded ovoids ofcompacted coal comprises: mixing together at least one binder, at leastone coal, and a particulate substituent made of at least one metal ormetal oxide to produce a paste; and compacting the paste into saidovoids.
 6. The process of claim 5, wherein:said particulate substitutentis selected from the group consisting of iron oxide, manganese ore,ferro-manganese, chromite, silica and quartz.
 7. Apparatus formanufacturing coke, comprising:a vertical furnace having a tubularenclosure with an upper part, a median part and a lower part; the upperpart including at an upper end a lock-type sealed charging inlet forcharging raw ovoids of coal into the upper part of said furance toprovide a bed which descends through said furnace, an outlet forrecovery of product gases, and an inlet for secondary recycled gas; themedian part including an electrical heater; and the lower part includingat a lower end a lock-type sealed discharging outlet for coke, and aninlet for a first stream of primary recycled gas; a cooling chamberhaving an inlet at one end connected to said discharging outlet of saidlower part of said vertical furnace, a lock-type sealed dischargigoutlet at an end opposite said one end for cold coke, an inlet at saidopposite end for a second stream of primary recycled gas, and an outletat said one end for secondary recycled gas; a first conduit connected tosaid outlet for recovery of product gases and conducting off a portionthereof as a product; a second conduit by which said outlet for recoveryof product gases is connected to said inlet for said first stream ofprimary recycled gas; a third conduit by which said outlet for recoveryof product gases is connected to said inlet for said second stream ofprimary recycled gas; and a fourth conduit by which said outlet forsecondary recycled gas is connected to said inlet for secondary recycledgas
 8. The apparatus of claim 7, wherein:said lock-type sealed charginginlet for raw ovoids of coal includes a rotating hopper having anopenable-closable distribution bell disposed in a lower part of saidhopper.
 9. The apparatus of claim 7, wherein:said lock-type sealeddischarging outlet for coke includes a sealed lock-compartment connectedbetween said lower end of said lower part of said furnace and said inletat said one end of said cooling chamber, and a rotatable hearth movablein vertical translation for opening and closing-off communicationbetween said lower end of said lower part of said furnace and said inletat said one end of said cooling chamber.
 10. The apparatus of claim 7,wherein:said tubular enclosure of said furnace includes peripheral wallmeans of refractory material in said median part, said wall meansdefining un upwardly facing shoulder means at which said tubularenclosure constricts in diameter; and said electrical heater includes atleast one pair of transversally-opposed electrodes disposed on saidshoulder means and being connected, outwardly through said tubularenclosure, to a means for supplying electrical power, whereby electricalenergy may be applied to said bed by passing an electrical currentbetween said electrodes via said bed and thereby resistively heat saidbed.
 11. The apparatus of claim 10, wherein:each of said electrodes isL-shaped so as to have a generally horizontal leg and a generallyvertical leg, each generally horizontal leg being disposed on saidshoulder means and projecting radially inwardly from the respective saidgenerally vertical leg, which projects upwardly adjacent said peripheralwall means, above said shoulder means.
 12. The apparatus of claim 7,wherein:said tubular enclosure of said furance includes peripheral wallmeans of refractory material in said median part, said wall meansdefining an upwardly facing shoulder means at which said tubularenclosure constricts in diameter; and said electrical heater includes:aperipheral electrode disposed on said shoulder means and beingconnected, outwardly through said tubular enclosure, to a means forsupplying electrical power, and a vertically extending central electrodeconnected outwardly through said furnace with said means for supplyingelectrical power; an inner enclosure housing said central electrodewhich, together with an upper exposed portion of said central electrode,has an ogival shape in elevation, and said inner enclosure is comprisedof a refractory material, whereby electrical energy may be applied tosaid bed by passing an electrical current between said electrodes viasaid bed and thereby resistively heat said bed.
 13. The apparatus ofclaim 12 wherein:said lock-type sealed discharging outlet for cokeincludes a sealed lock-compartment connected between said lower end ofsaid lower part of said furance and said inlet at said one end of saidcooling chamber, and having a rotatable hearth movable in verticaltranslation for opening and closing-off communication between said lowerend of said lower part of said furance and said inlet at said one end ofsaid cooling chamber; said central electrode being mounted via saidinner enclosure on said rotatable hearth for vertical translationtherewith for adjusting said exposed portion of said central electrodein height relative to said peripheral electrode.
 14. The apparatus ofclaim 10, wherein:said tubular enclosure is of rectangular transversecross-sectional shape.
 15. The apparatus of claim 7, wherein:saidtubular enclosure of said furnace includes peripheral wall means ofrefractory material in said median part; and said electrical heaterincludes an external induction coil disposed in said refractory materialso as to be coaxial with said tubular enclosure in said median part,said induction coil being connected with an external means for supplyingelectrical power for inducing an electromagnetic field said bed.
 16. Theapparatus of claim 15, wherein:said electrical heater further includesan internal laminated magnetic core; and an internal induction coilwould on said internal laminated magnetic core; an inner enclosurehousing said internal laminated magnetic core; said inner enclosure,together with said internal laminated magnetic core, having an ogivalshape in elevation; said inner enclosure is comprised of a refractorymaterial and said external induction coil and said internal inductioncoil being connected to said external means for supply electrical powerand providing said coils with electrical power in phase with oneanother.
 17. The apparatus of claim 7, wherein:said tubular enclosure ofsaid furnace includes peripheral wall means of refractory material insaid median part; and said electrical heater includes a group of pairsof external radially-acting induction coils disposed in said refractorymaterial, said external induction coils of each pair being diametricallyopposed transversally of said tubular enclosure and said pairs beingequiangularly spaced from one another angularly of said tubularenclosure, so that said group of pairs, collectively, are coaxial withsaid tubular enclosure in said median part, said pairs of inductioncoils being connected to respective phases of an external means forsupplying polyphase electrical power for inducing an electrical magneticfield said bed which revolves angularly around said furnace.
 18. Theapparatus of claim 17, wherein:said electrical heater further includes agroup of pairs of internal, radially-acting induction coils, saidinternal induction coils of each pair being diametrically opposedtransversally of said tubular enclosure and said pairs of internalinduction coils being equiangularly spaced from one another angularly ofsaid tubular enclosure, so that said group of pairs of internalinduction coils, collectively are coaxial with and centrally located insaid tubular enclosure in said median part, each pair of said internalinduction coils being disposed in radially spaced confronting relationwith a respective pair of said external induction coils; an externalmeans for supplying polyphase electrical current; confronting pairs ofsaid internal and external induction coils being connected withrespective same phases of said external means for supplying polyphaseelectrical current, thereby providing a group of pairs of coupled coilswhich cooperate so as to generate a rotating field said bed; and aninner enclosure housing said internal induction coils; said innerenclosure, together with said internal induction coils, having an ogivalshape in elevation; said inner enclosure is comprised of a refractorymaterial.
 19. The apparatus of claim 15, wherein:said peripheral wallmeans defining an upwardly facing shoulder means at which said tubularenclosure constricts in diameter; said shoulder means being locatedabove said external induction coil disposed in said wall means; and saidelectrical heater further comprises at least one pair oftransversally-opposed electrodes disposed on said shoulder means andbeing connected, outwardly through said tubular enclosure, to a secondexternal means for supplying electrical power, whereby electrical energymay be applied to said bed by passing an electrical current between saidelectrodes via said bed and thereby resistively heat said bed.
 20. Theapparatus of claim 17, wherein:said electrical heater further includes avertically extending central electrode connected outwardly through saidtubular enclosure to said second external means for supplying electricalpower; an inner enclosure housing said central electrode, which,together with an upper exposed portion of said central electrode, has anogival shape in elevatin, and said inner enclosure is comprised of arefractory material, whereby electrical energy may be applied to saidbed by passing an electrical current between said transversely - opposedelectrodes and said central electrode via said bed and therebyresistivity heat said bed.